1. Field of the Invention
The present invention relates to a workpiece feeding apparatus for a plate processing machine, and more specifically to a work feeding apparatus for a plate processing machine which can locate work at high speed.
2. Description of the Prior Art
FIG. 1 shows a typical example of a workpiece feeding apparatus mounted on a worktable for a punch press, for instance.
In more detail, a ball screw 103 extending in a workpiece feed direction (the right and left in FIG. 1) is rotatably supported by two bearings 101L and 101R. This ball screw 103 is rotated by a drive motor 107 mounted on one (e.g., left) side of the ball screw 103 via a gear mechanism 105, for instance. On the other hand, a ball nut 115 in mesh with the ball screw 103 is attached to the lower surface of a worktable 113. The worktable 113 is provided with a slider 111 movable along a guide rail 109 fixed so as to extend in the workpiece feed direction.
Therefore, when the motor 107 is driven, since the ball screw 103 is driven or rotated by the motor 107 via the gear mechanism 105, the ball nut 115 is moved along the ball screw 103, so that worktable 113 can be moved in both the rightward and leftward in the workpiece feed direction.
In the above-mentioned prior art workpiece feeding apparatus, the maximum speed of the worktable 113 for clamping workpiece W is decided on the basis of both the maximum number of revolutions of the drive motor 107 and the lead of the ball screw 103. In this case, however, since there exists a limit of the maximum number of revolutions of the drive motor 107, when the feed speed is required to increase, it is necessary to increase only the lead of the ball screw 103.
When the lead of the ball screw 103 is simply increased, since an inertia (i.e., load) of the motor shaft increases, the output torque required for the drive motor 107 also increases. On the other hand, however, since there exists a limit of the output torque of the drive motor 107, there exists a problem in that it is impossible to simply increase the lead of the ball screw 103, as with the case of the punch press in which high acceleration or high deceleration motion is often required for the worktable, in particular.
Here, it should be noted that the maximum speed of the ball screw and the worktable feeding efficiency are different from each other. In more detail, FIG. 2A shows the worktable speed when the ball screw 103 of a small lead is used, and FIG. 2B shows the worktable speed when the ball screw 103 of a large lead is used, on condition that the output torque of the drive motor 107 is the same. In the case shown in FIG. 2A, although the total time t1 from when the worktable 113 begins moving to when it stops moving is relatively short, the maximum speed Vmax of the ball screw 103 is low. In the case shown in FIG. 2B, although the maximum speed Vmax of the ball screw 103 can be increased, the total time t2 from when the worktable 113 begins moving to when it stops moving is relatively long. In other words, when the lead of the ball screw 103 is simply increased as shown in FIG. 2B, although the maximum speed Vmax can be increased, since the acceleration of the motor 107 is low, a long time is required from when the worktable 113 begins moving to when it stops moving, with the result that the work feeding efficiency becomes low on the contrary. On the other hand, since there exists a limit of the maximum torque of the drive motor 107, it is impossible to increase the acceleration of the worktable 113.